EP0341580B1 - Process for purifying by distillation mercury-containing materials or mixed materials - Google Patents

Abstract

The invention relates to a process for purifying mercury-containing materials or material mixtures by distillation and/or to the recovery of mercury therefrom, which is characterised in that the charge material is, as a solid/liquid suspension or solution, injected into the distillation apparatus or atomised and/or sprayed therein, preferably by means of a rotary atomiser, and in that it is carried out at a pressure less than 1 bar, at a pressure reduced as compared with atmospheric pressure or in vacuo, and that the charge material is kept in motion. <IMAGE>

Description

The present invention relates to a method for the purification by distillation of mercury-containing substances and / or substance mixtures and / or for the production of mercury.

The process is carried out continuously with moving feed material at pressures which are substantially below atmospheric pressure or in a vacuum. This enables low distillation temperatures below 400 ° C, which allows indirect heating of the apparatus.
The feed containing mercury is first milled wet and then sprayed as a suspension into a thin-film evaporator, preferably using a rotary atomizer.
The sprayed-in suspension is heated on the indirectly heated inner wall of the thin-film evaporator, causing gases and vapors containing mercury to rise.
The feed layer adhering to the wall of the thin film evaporator is constantly scraped off by a rotating device.
The mercury-containing vapors are removed from the upper area of the thin-film evaporator and passed on to a condensation device, while the solid components of the original suspension are removed from the thin-film vacuum evaporator below.

DE-OS 22 10 759 describes a process for the recovery of mercury from aqueous solutions, especially for removing small traces of mercury from an exhausted brine solution which emerges from the electrolytic cells in the mercury process. The solution is treated with a chemical reducing agent, the finely divided or colloidal mercury obtained is removed by steam distillation, the mixed steam is condensed, and the mercury is separated from the condensate.

The state of the art is also to be mentioned in GB-PS 15 24 446, the cleaning of mercury-containing sludges, the sludge at a temperature of 200-350 ° C, preferably at a reduced pressure of minus 0.06 to minus 0.10 Atmospheres are heated, the steam thus obtained is condensed at subatmospheric pressure at a temperature preferably of 20-50 ° C and further traces of steam at superatmospheric pressure, preferably of 2-3 atmospheres and a temperature of 5-35 ° C are condensed.

The "Textbook of Metallurgy", by Tafel, Victor and Wagemann, Karl, Volume 1, S.Herzel Verlags- Buchhandlung, Leipzig 1951, is also to be mentioned in relation to the state of the art , as well as furnace types, including rotary tube furnaces for roasting or mercury distillation from ores.

The state of the art also includes Gmelin's handbook of inorganic chemistry, 8th edition, system no.34, relating to mercury, published by Verlag Chemie, Weinheim / Bergstrasse, 1960. There, the drying of mercury-containing sludge in a vacuum is described accordingly Japanese Patent 1,334,346 (1939). This manual also describes vacuum distillation for cleaning metallic mercury.

The Japanese patent JP-A-54-102 229 for the recovery of mercury from activated carbon should also be mentioned in relation to the prior art. To avoid dust formation during the distillation of mercury, binders such as water glass are added.

The textbook "Chemical Technology" by Winnacker + Küchler, 4th edition Volume 1, pages 156 and 157. There is shown a vertical thin-film evaporator which is described as being well suited for the evaporation of temperature-sensitive products which may only be subjected to thermal stress for a short time. A shaft with fixed or pendulum-mounted wipers rotates in the tube, which is heated by a jacket. The liquid to be evaporated is fed in at the upper end. The wipers maintain a constant film thickness. Under certain circumstances, such apparatus can be evaporated to the dry product.

The procedure according to the prior art is described below on the basis of working up Hg-containing activated carbon or the extraction of metallic mercury from ores or concentrates.
Processes for the production of mercury by dry distillation from substances containing mercury are known from the smelting of ores or minerals containing mercury. It is also known to purify mercury-containing residues, for example from acetaldehyde electrolysis or activated carbon sludges from chloralkali electrolysis, by such dry distillation from mercury. These prior art methods include that the feed is dried as much as possible before being introduced into the distillation apparatus so as not to have to also additionally apply the heat of vaporization for the water in the distillation process, which water must accordingly be removed beforehand by drying. If, for example, the raw material was enriched by flotation in mercury smelting, the aim is to reduce the moisture content to approximately 8 to 10% before using the material in the distillation or roasting furnace. According to the prior art, residues containing mercury are also dewatered by mechanical separation processes before the mercury is thermally treated on the feed material is removed by distillation; for example, mercury-containing sludges from chlor-alkali electrolysis are reduced to approx. 20 to 45% by weight in the moisture content by filter presses.

The known distillation apparatus for the production of mercury or the purification of mercury can be differentiated according to whether and how the feed material is moved during the distillation process.

In one variant, the material is not moved. It rests in one or more layers either directly on the walls of the distillation apparatus or on sheets to which it was previously applied and which are then introduced into the distillation apparatus. These apparatuses are preferably used when fine-grained or powdery material is treated in order to keep the dust discharge low with the vapors and gases which are derived from the distillation apparatus. This known method is a batch operation with the heating of inert masses.

In another variant, the material is moved slightly during the distillation process, but migrates through the distillation apparatus during the process. This principle is preferably used in the smelting of minerals containing mercury, e.g. in shaft furnace with or without internals.

A third variant involves moving the material during the distillation process in order to improve mass and heat transfer processes during the distillation process.
For this purpose, rotary kilns are known in the prior art. These work by one with its axis horizontally positioned or slightly inclined against the horizontal rotating tube rotates slowly about its axis.
As a result, the goods always come into contact with new parts of the wall or, in contrast to a dormant layer, are always exposed to the furnace atmosphere with a different surface. When arranged horizontally, rotary kiln devices are usually loaded and emptied in batch mode. In the case of a slightly inclined arrangement, the material to be treated travels in the direction of inclination of the axis through the rotary kiln, the residence time being determined by the set speed. It is also known to install internals inside the rotary tubes, which are intended to prevent the material from being crushed and to support movements of the material.

• bei Atmosphärendruck oder leichtem Unterdruck
• oder im Vakuum durchgeführt wird.

Für die oben angeführte Apparatur ist beides bekannt. Die bekannten Apparate zur Behandlung quecksilberhaltiger Stoffe werden etwa bei Atmosphärendruck betrieben. Es wird ein leichter Unterdruck eingestellt, der zum Zweck hat, Leckagen von der Ofenatmosphäre nach außen zu verhindern, zur Verhinderung von Quecksilberverlusten an die Umgebung, ebenso wie aus Gründen des Arbeitsschutzes wie auch zur Erhöhung der Quecksilberausbeute. Der Unterdruck im Destillationsapparat beträgt in der Regel nur einige Millimeter Wassersäule, nicht jedoch weniger als 0,9 bar absoluten Druck.The known methods for the distillation treatment of mercury-containing substances can also be differentiated according to whether the distillation

• at atmospheric pressure or slight negative pressure
• or is carried out in a vacuum.

Both are known for the above-mentioned apparatus. The known apparatus for treating mercury-containing substances are operated at about atmospheric pressure. A slight negative pressure is set, which has the purpose of preventing leaks from the furnace atmosphere to the outside, to prevent mercury losses to the environment, as well as for reasons of occupational health and safety and to increase the mercury yield. The vacuum in the distillation apparatus is usually only a few millimeters of water, but not less than 0.9 bar absolute pressure.

It is also known that during the distillation of mercury-containing substances, dust formation from the material causes problems in the downstream condensation. It is known from the extraction processes of mercury smelters that the condensation product always becomes more or less largely consists of a damp or muddy material interspersed with metallic mercury, which is called "Stupp". In processes according to the prior art, the formation of stupps is favored by the following factors: presence of carbon, fine-grained loading and when the goods are moved.

In the known methods, the distillation furnaces are heated either directly, for example by flames or flue gases, or indirectly via one of the walls, for example by flames or electrically.
The processes that work at atmospheric pressure or slightly negative pressure to reduce the leakage, and that is essentially all in which the material is moved during the distillation process, require high temperatures, above about 400 to 600 ° C.
Otherwise the residual mercury content in the treated substances is too high.
At this temperature level, the introduction of the required heat in indirect heat exchange by condensing steam from a heating medium or by releasing the heat of a heat transfer fluid is technically not possible under economic conditions. Working in a vacuum is known for distillation ovens in which the material is not moved during the distillation process. Under these conditions, indirect heating with equipment such as water vapor or heat transfer oil is known. Such heating is desirable because it gives better heat transfer coefficients than heating with gaseous media. Overall, indirect heating is desirable, because with direct heating the amount of exhaust gas increases and the mercury losses increase due to the partial pressure of mercury. This is the main source of loss in mercury smelters. With direct heating, there is also a greater risk of dust being entrained due to higher flow rates in the furnace.
There is also a fire risk if mercury-containing activated carbon is to be freed from mercury.

Distillation furnaces with essentially static goods have the disadvantage of poor heat and mass transfer.
Layers can crust over, especially in the case of fine-grained substances such as activated carbon in powder form. There is no adequate transport mechanism due to the dormant layer of material to create a sufficient partial pressure gradient for mercury. This results in long treatment times in the ovens. The reduction in the water content before introduction into the distillation apparatus, which is customary in the prior art, should also be considered with regard to dust formation in the distillation apparatus and introduction of dust into the condensation stage. By reducing the water content in the feed, the amount of water evaporating in the still is to be reduced. In the case of directly heated stoves, the amount of flue gas can be kept lower. In the case of indirectly heated ovens, especially those with a stationary material, the oven throughput time can be reduced.

• durch Strahlung von den Heizelementen an die Haube,
• von der Haube wiederum durch Strahlung an die Horden,
• von diesen durch Wärmeleitung und Strahlung an das Aufgabegut.

In the prior art, heating and evaporation takes place, for example, via electrical heating elements which are arranged in the interior of the furnace. Heat transfer takes place:

• radiation from the heating elements to the hood,
• from the hood to radiation to the hordes,
• of these through heat conduction and radiation to the feed.

Large ballast masses of steel must be warmed up and cooled for each batch. This is very energy intensive. In addition, due to the sluggish heat transfer processes, only one furnace can be charged in 24 hours.
To be sufficient at the prevailing atmospheric pressure To de-quench the material, heating temperatures up to 550 ° C must be achieved. The residual content in the treated goods is in the range of about 20 to 50 mg Hg per kg of material. A further reduction is limited by the lack of mass transfer mechanisms in the atmosphere inside the hood with the resting layer of feed material on the tray trays. The construction is not capable of moving the goods. It also prohibits this principle of the process, because after the water has evaporated (many A-coals come from wet filtration and still carry moisture) there is otherwise the risk of exothermic reactions due to deflagration or fire. In addition, too much activated carbon dust is entrained in the downstream injection condensation.
The furnace heating is switched off when the shift of the system operated in single shift operation ends.
The ovens are left with the trolleys and the feed material until the start of the shift the next morning for cooling by natural convection. In order to be able to reload and heat the ovens in a 24-hour cycle during the shift, the emergency vehicles must be changed at the beginning of the shift. For this purpose, the flange connection for exhaust gas cleaning must be loosened on the emergency vehicle that has not yet cooled to ambient temperature. The emergency vehicle, which is pulled out of the oven by muscle power, is then left to cool down further. The liquid mercury, which has accumulated in the collecting tube under the emergency vehicle, is drained by gravity in the open river into a collecting vessel, driven by forklift to the collecting container of the Hg filling and drained there.
The many open handling of material containing mercury or mercury, sometimes at elevated temperatures, is problematic for occupational safety. There is a problem with the MAK values for Hg at the busy To comply with personnel.
After the stack of trays has cooled down on the oven service trolley, the hood is pulled. The tray trays on the emergency vehicles are transported to the emptying site by forklift trucks. The treated material is transferred into transport packaging for the landfill using a vacuum suction system.

The methods of the prior art only allow inadequate cleaning of mercury-containing substances or mixtures of substances. They are harmful to the environment and people and are time-consuming and costly.

The present invention has for its object to provide a method for the purification of mercury-containing substances or mixtures of substances by distillation, which enables extensive cleaning of the feed material, is environmentally friendly and does not burden people, which can be operated continuously and which is energy-efficient.

This object is achieved according to the invention by a method of the type mentioned at the outset in that the feed material is injected as a solid / liquid suspension or solution into a thin-film evaporator or is atomized or sprayed therein, preferably by a rotary atomizer.

Such thin-film evaporators are known according to the prior art described at the outset. Such a vertical thin-film evaporator with indirect wall heating is shown in the literature reference "Chemical Technology" from Winnacker + Küchler, inside which a shaft rotates, on which wipers are attached, which scrape off the feed material from the inner walls of the thin-film evaporator. The one to be evaporated Liquid is introduced into the thin film evaporator at the top and the solid components can be removed at the bottom.

It is not yet known to operate thin-film evaporators for mercury, in which the material is moved during the distillation process, in a vacuum or at <1 bar, in order to be able to carry out indirect heating with condensing water vapor and / or a heat transfer fluid. The resulting high heat transfer numbers are a prerequisite for the larger amount of moisture to be evaporated inside the thin film evaporator.

It is an essential feature of the present invention that such a known thin-film evaporator is used for its implementation, which is operated in a vacuum or at <1 bar.

Due to the movement of the goods for better heat and mass transfer, the continuous process control offers advantages compared to dormant layers of a batch process. The disadvantages of rotary kilns are thus avoided, in which the good movement results in a greater dust discharge, which leads to a corresponding formation of stumps in the condensation devices.

Due to the possibility of working in a vacuum or at <1 bar, indirect heating with steam and / or a heat transfer fluid can be achieved in the method according to the invention, because the vapor pressure of the mercury then enables a sufficiently low residual mercury content in the treated material at temperatures below 400 ° C. The lower temperatures simplify the choice of materials for the thin-film evaporator, and there are requirements for the mechanical implementation of the rotating Built-in fittings for scraping the goods off the wall.
The disadvantage of dormant layers of the material to be treated with poor heat and mass transfer ratios is avoided.
The batch operation typical of stills with still layers is also avoided, in which larger and larger masses of the furnace construction must be heated and cooled as ballast when heating up and cooling down. Health hazards for the operating personnel when handling mercury-containing material during the mostly manual loading are avoided.

In particular, powdery mercury-containing substances or those in which abrasion can easily occur can be used with the method according to the invention. It can e.g. are activated carbons loaded with mercury, which at the same time also contain the carbon that promotes stupp formation.

In the process according to the invention, a solid-liquid suspension is produced by the targeted addition of liquid with such a high liquid content in the slurry that the suspension can be sprayed in a thin-film evaporator.
Before being used in the thin-film evaporator, the suspension is wet-ground in order to set an optimal particle size and particle size distribution.
The liquid of the sprayed-in suspension has a washing effect on the vapors and gases passing in countercurrent in the upper part of the thin-film evaporator, thus reducing the dust discharge to a tolerable level.
At the outlet end of the thin-film evaporator, a gaseous medium is specifically introduced into the evaporator in order to transport mercury in the part as entraining gas to improve the thin film evaporator in which the suspension has largely evaporated.

• 1. Verdampfung der Flüssigkeitsmenge bei nicht zu hohen Temperaturen.
• 2. Reduzierung des Restgehaltes an Quecksilber bei höheren Temperaturen in dem von der Flüssigkeit befreiten Aufgabegut.

In the interior of the thin-film evaporator, two different process engineering tasks that are important for the process had to be solved in the direction of movement of the feed material:

• 1. Evaporation of the amount of liquid at not too high temperatures.
• 2. Reduction of the residual mercury content at higher temperatures in the feed material freed from the liquid.

For the first of these tasks, the requirement for the transfer of large amounts of heat for the evaporation of the liquid applies, this is provided in the method according to the invention on the equipment side by heating by means of condensing steam. For the second of these tasks it applies that no large amounts of heat are to be transferred and that indirect heating with an organic heat transfer fluid is provided in the method according to the invention.

• Kohlenstoffgehalt,
• Feinkörnigkeit,
• Bewegung im Destillationsapparat.

With the method according to the present invention, mercury can be obtained from substances containing mercury.
Furthermore, gases or vapors are led to the condensation stage, which contain little dust due to the washing effect of the sprayed-in suspension. Without this washing effect, the intended movement of the feed material in the thin-film evaporator would not be possible, since too much dust would be discharged, especially when treating activated carbon, which is already in powder form, has been ground or has been given the appropriate dust content by abrasion of granular coal. Especially when it comes to the treatment of activated carbon, all the features are present which, according to the known state of the art, favor stupp formation:

• Carbon content,
• Fine grain,
• Movement in the still.

In contrast to a rotary kiln of a rotary kiln, the equipment rooms for indirect heating can easily be attached to a stationary jacket of a thin-film evaporator. While in the rotary tube the lower and side part covered with material always causes the heat transfer from the rotating jacket to the material to be treated, with the method according to the invention practically the entire jacket surface is effective as a heat exchange surface when the thin-film evaporator is arranged vertically. Due to the constant peeling of the material layer building up on the jacket by the rotating internals, a smaller layer thickness is also realized on the wall than occurs in the rotary kiln, whereby the heat and mass transfer ratios are further improved. This combination of advantages is made possible by a combination of process features, which is in contrast to the known processes. So far, in order to keep the amount of liquid to be evaporated in the distillation furnaces apart from the mercury, the feed material has been largely dewatered or dried; at most, wetting has taken place to reduce the dust discharge. In contrast, the opposite is done in the method according to the invention. In a pretreatment stage, a solid-liquid suspension is produced by adding specific liquids, with such a high liquid content in the slurry that the suspension can be sprayed in a thin-film evaporator.

• einer ersten Stufe im indirekten und/oder direkten Wärmetausch mit einem oder mehreren kälteren Kühlmedien in entsprechenden Apparaten und Ausschleusung einer ersten flüssigen Phase aus dem verbleibenden Dampf-/Gas-Strom in einem ersten Abscheider zur Trennung des Quecksilbers von der leichteren flüssigen Phase und
• einer zweiten Stufe, ausgebildet als Direktkondensation im Wärme- und Stoffaustausch mit einer Flüssigkeit,

daß die zweite Stufe als Waschkolonne ausgeführt ist, vorzugsweise mit einer Füllkörperschüttung und die flüssige Phase über einen zweiten Abscheider ausgeschleust wird,
daß der Waschflüssigkeit eine Substanz zugesetzt wird zur selektiven Erhöhung der Absorption von Quecksilber,
daß die Direktkondensation mit einer Temperatur der Aufgabeflüssigkeit am Kopf der Kolonne arbeitet, die ≦ (kleiner/gleich) 6°C ist, und daß damit der Partialdruck des Hg in den beim Verlassen der Kolonne nicht kondensierten Gasen stark reduziert wird,
daß die Direktkondensationsstufe zweistufig ausgeführt wird mit

• einer unteren Stufe, in der die Umlaufflüssigkeit durch ein Kühlmedium rückgekühlt wird, das eine Vorlauftemperatur ≧ (größer/gleich) 6°C hat,
• und einer zweiten Stufe, in der die aufgegebene Flüssigkeit mit einer Temperatur ≦ (kleiner/gleich) 6°C aufgegeben wird.

The method according to the invention is further characterized in that
that at a pressure lower than 1 bar, or working in a vacuum,
that the feed is moved
that the liquid phase begins to boil at lower temperatures than mercury,
that the feed has a dry matter content of ≦ (less than or equal to) 42% by weight, preferably from 10 to 30% by weight,
that the feed material has been warmed up to such an extent before it is introduced into the thin film evaporator that the temperature level is not lower than 10 K below the evaporation point of the earliest boiling liquid constituents of the suspension - calculated at the absolute pressure prevailing in the thin film evaporator, preferably at or above this temperature , but not higher than would correspond to a spontaneous evaporation of 10% of the liquid when relaxing to the pressure prevailing in the thin-film evaporator,
that a gaseous medium is introduced at the outlet end of the thin-film evaporator in order to improve the mass transport for mercury in the part of the thin-film evaporator in which the suspension has largely evaporated, and that the suspension is wet-milled before use in the thin-film evaporator is used to set an optimal grain size and grain size distribution.
The method is further characterized in that
that the vaporized substances flow through the thin-film evaporator in countercurrent to the direction of the feed,
that at least two different temperature levels are selected for the equipment rooms, adapted to the various process engineering tasks to be solved in the thin-film evaporator,
that at the beginning of the conveying path of the feed material in the thin film evaporator a low temperature level prevails, preferably for the evaporation of the liquid phase of the suspension and a higher temperature level on the way of the feed material downward in the thin-film evaporator in order to achieve the lowest possible mercury content in the feed material which leaves the thin-film evaporator,
that the feed material in the form of a suspension is thrown onto the indirectly heated jacket of the thin-film evaporator and mechanically scraped off before the formation of a thick layer, which would hinder the heat and mass transfer, and downwards in the conveying direction of the feed material again from other parts of the rotating device onto the jacket of the Thin film evaporator is spun,
that fractional condensation is carried out with

• a first stage in indirect and / or direct heat exchange with one or more colder cooling media in appropriate apparatus and discharge of a first liquid phase from the remaining steam / gas stream in a first separator for separating the mercury from the lighter liquid phase and
• a second stage, designed as direct condensation in the heat and mass exchange with a liquid,

that the second stage is designed as a washing column, preferably with a packed bed, and the liquid phase is discharged via a second separator,
that a substance is added to the washing liquid to selectively increase the absorption of mercury,
that the direct condensation works at a temperature of the feed liquid at the top of the column which is ≦ (less than or equal to) 6 ° C., and that the partial pressure of the mercury in the gases which are not condensed when leaving the column is greatly reduced,
that the direct condensation stage is carried out in two stages

• a lower stage, in which the circulating liquid is recooled by a cooling medium that has a flow temperature ≧ (greater than or equal to) 6 ° C,
• and a second stage, in which the applied liquid is applied at a temperature ≦ (less than or equal to) 6 ° C.

Further features of the method according to the invention consist in
that it is used for the regeneration of activated carbon, that a washing effect is exerted on occurring and discharged gases and vapors,
that the thin-film evaporator is designed as a cylindrical container so that its inside length is at least four times as large as the inner diameter and that it has a fixed jacket 3 and a rotating device 4 inside the same.
This serves to move and convey the feed material, as well as scraping or scraping the same off the jacket of the thin-film evaporator and to prevent free dropping of the feed material after scraping up to the end of the thin-film evaporator, which is arranged vertically. The rotating device 4 also serves to bring the feed material back into contact with the jacket 3 at another point.

Further features of the device consist in the fact that the walls of the thin-film evaporator are largely designed as double jackets or are equipped on the outside with welded pipe coils,
that the outer wall of the thin-film evaporator is equipped with at least two operating rooms, that the lower temperature level on the operating side is generated by condensing water vapor in the first operating room 5 at a pressure of 2 to 25 bar, preferably 10 to 12 bar - and the higher by heating the operating rooms 6 and 7 with an organic Heat transfer fluid in the temperature range from 250 to 370 ° C, preferably 300 to 350 ° C,
that the vacuum generating device, preferably as a water ring pump, is arranged between the first and second condensation stages.

In the method of the present invention, for example, an mercury-containing activated carbon suspension is introduced into the thin-film evaporator and freed of mercury by treatment in the manner described and is therefore regenerated for reuse in adsorption processes or can be further disposed of by incineration or landfill without this mercury content be fed.

The designs of the walls of the thin-film evaporator are used to keep the jacket temperatures at nominal operation above the dew point of vapors, which are evaporated from the feed material, and as an operating room for vaporous or liquid heating agents for the transfer of the heat of vaporization and the sensible heat in indirect heat exchange to serve the wall of the thin film evaporator to the feed.

When the evaporated substances flow according to the invention in countercurrent to the direction of travel of the feed material through the thin-film evaporator, a mass and heat exchange takes place in such a way that the finely introduced feed material in the form of a suspension has a washing action for the mercury vapors flowing in countercurrent, vapors of the in the suspension existing liquids and gases that were dissolved in the suspension or were specifically introduced into the thin-film evaporator at the outlet end of the feed material.
This results in a reduction of the dust-like impurities that would otherwise be caused by the vapors or Steam / gas mixture would be discharged from the thin film evaporator. In addition to the chosen process, this is achieved by the chosen liquid content of the feed material in suspension form. This liquid content prevents dry dust from being present in the area of the feed zone of the suspension, in which vapors or a gas / vapor mixture are drawn off from the thin-film evaporator, as a result of which a largely mercury-free and liquid-free dry substance is released at the end of the thin-film evaporator the treated feed leaves it.

The division of the thin-film evaporator has the effect that impurities from the thin-film evaporator preferably fail in the first stage and therefore do not contaminate the washing liquid in the second stage and pure Hg is obtained.

Batches which do not reach the intended residual mercury content, but which contain between 0.6 and 50 mg / kg, are sent to the landfill. Faulty batches with residual mercury levels> 50 mg / kg are treated again in the plant.

• einen Wärmetauscher zur Wärmerückgewinnung im Warmwasser,
• einen Einspritzkondensator mit indirekter Wasserkühlung,
• eine Vakuumpumpe,
• eine Wasserwäsche in einer Waschkolonne mit Füllkörpern, wobei das in der letzten Stufe aufgegebene Frischwasser durch Kaltwasser eines Kältemaschinenprozesses gekühlt wurde. Dadurch wird der Partialdruck für Hg im nicht kondensierten Abgas sehr weit abgesenkt,
• eine Abgasreinigung mit den einzelnen Verfahrensstufen
  • . Säurewäsche mit Schwefelsäure
  • . Laugenwäsche mit Natronlauge
  • . Wasserwäsche
  • . Aufwärmung durch indirekten Wärmetausch mit Warmwasser auf 20°C über dem Wassertaupunkt (damit die anschließende Adsorptionsstufe einwandfrei funktiniert),
• einen Aktivkohle-Adsorber.

The substances evaporating from the activated carbon, essentially mercury and water, pass through at the upper end of the thin-film evaporator after they have emerged

• a heat exchanger for heat recovery in hot water,
• an injection condenser with indirect water cooling,
• a vacuum pump,
• a water wash in a washing column with packing, the fresh water added in the last stage being cooled by cold water from a refrigerator process. As a result, the partial pressure for Hg in the uncondensed exhaust gas becomes very wide lowered,
• exhaust gas purification with the individual process stages
  • . Acid wash with sulfuric acid
  • . Wash with caustic soda
  • . Water wash
  • . Warming up by indirect heat exchange with hot water to 20 ° C above the water dew point (so that the subsequent adsorption stage works perfectly),
• an activated carbon adsorber.

In this way, substances evaporated from the activated carbon are removed from the exhaust gas, in particular the residual Hg value of the latter is brought below 0.001 mg / m³ of exhaust gas.

The cleaned exhaust gas is released into the atmosphere via an exhaust gas chimney.

The liquids condensed out in the condensation stages - essentially water and mercury with impurities - are separated by decantation. The water is fed to a process water collection container. From it, the amount of water required for the preparation station is used again. The rest are then cleaned and then stored in a container for clean process water to e.g. to be used again as washing water in the process or in the drum washing station. Excess quantities are discharged into the sewage system as waste water after cleaning.

The separated mercury is weighed in a weighing station so that the recovered mercury can be assigned to the processed customer batches. Then it is collected in a buffer container. From there it is further cleaned - if it is necessary for the respective application - and ready for dispatch in the filling station in the standard 36.5 kg steel containers bottled.

• 1. Die Austreibung des Hg aus dem Aufgabegut erfolgt in einem geschlossenen, dichten Dünnschichtverdampfer unter Vakuum. oder bei < 1 bar. Dadurch kann anstelle einer elektrischen Beheizung bei Normaldruck und 550°C mit einer organischen Wärmeträgerflüssigkeit von 360°C in der Endstufe beheizt werden. In der Eingangszone, in der vor allem Wasser zu verdampfen ist, kann der gute Wärmeübergang der Wasserdampfkondensation ausgenutzt werden.
• 2. Bei Undichtigkeiten im Dünnschichtverdampfer kann nur Leckluft nach innen gelangen, es können aber keine Hg-Dämpfe nach außen dringen. Die Sicherheit des Anlagebetriebs für Arbeitsschutz- und Emissionsschutzbelange wird dadurch wesentlich erhöht. Bei bisherigen Verfahren bestand beim Eindringen von Luft Brandgefahr in der letzten Ausheizphase, in der wasserfreie Aktivkohle Temperaturen über 500°C ausgesetzt war. Diese Brandgefahr ist beim erfindungsgemäßen Verfahren infolge tieferer Prozeßtemperaturen des Vakuumbetriebes bzw. bei < 1 bar nicht gegeben.
• 3. Die im oberen Teil des Dünnschichtverdampfers abgezogenen Wasser- und Hg-Dämpfe werden von dem eingespritzten wässrigen Aufgabegut in Form einer Suspension einer Wäsche unterzogen. Dadurch wird weniger festes Material in die anschließenden Verfahrensstufen der Kondensation verschleppt. Trockener Aktivkohlestaub, der am leichtesten von einem Gas-/Dampfstrom mitgetragen wird, kommt im oberen Teil des Dünnschichtverdampfers gar nicht vor. Dies ist ein wesentlicher Vorteil dieses kontinuierlich beschickten Dünnschichtverdampfers gegenüber dem Chargenprozeß in einem Ofen, wo nach der Phase des Verdampfens von Wasser immer trockene Aktivkohle im Bereich des Gas-/Dampf-Abzugs liegt.
• 4. Im Dünnschichtverdampfer gemäß diesem Verfahren findet ein intensiver Stoff- und Wärmeaustausch statt durch
  • feine Zerstäubung der für diesen Zweck aufgeschlämmten Suspension. Das Aufgabegut liegt nicht in einer ruhenden Schicht auf Hordenblechen,
  • ständige Verwirbelung und Bewegung des aufzuarbeitenden Materials. Es entstehen keine an der Oberfläche verkrustenden Schichten, die Stoff- und Wärmeübergang der fiefer liegenden Schichten stark behindern, wie dies bei einem chargenweise mit Horden beschickten Ofenprozeß der Fall ist,
  • verdampfendes Wasser als Transportmedium für Hg. Beim Ofenprozeß verbot sich eine weitere Wasserzugabe wegen der hohen elektrischen Heizkosten für die Verdampfung desselben,
  • über den Kühler in den unteren Teil des Dünnschichtverdampfers gezielt eindosiertes Strippgas als Transportmedium bzw. zur Verstärkung des Partialdruckgefälles für Hg im unteren, wasserfreien Bereich. Eine solche Zugabe von Strippgas war beim chargenweise betriebenen Ofenprozeß nicht möglich, weil zu viel Aktivkohlestaub mitgerissen würde bzw. bei den hohen Temperaturen bei Luftzugabe Brandgefahr auftreten würde.
  Auf diese weise sind deutlich geringere Rest-Hg-Gehalte zu erzielen als beim dem Chargen-Ofenprozeß und es wird die Erwartung gerechtfertigt, daß das behandelte Gut wie Kohlestaub verbrannt werden kann und nicht als Abfall deponiert werden muß.
• 5. Es handelt sich um einen kontinuierlichen Prozeß, in dem
  • nicht wie bei jeder Charge große Stahlmassen als Ballast mit aufgewärmt und abgekühlt werden müssen und bei dem praktisch keine Möglichkeit zu einer Wärmerückgewinnung gegeben war,
  • die Transporte des Aufgabeguts vom Ansatz bis zur Abfüllung in geschlossenen Ausrüstungen durch maschinelle Einrichtungen erledigt werden -und nicht durch Handarbeit des Bedienungspersonals. Damit wird ein wesentlich höheres Maß an Vorsorge hinsichtlich Arbeitssicherheit und Arbeitsschutz für das Bedienungspersonal als inhärente Eigenschaft dieses Verfahrens realisiert.
    Die Einhaltung der biologischen Arbeitsstoff-Toleranzwerte für Hg beim Bedienungspersonal wird dadurch wesentlich besser möglich, als es unter den Verhältnissen des bisherigen Verfahrens der Fall sein konnte mit seinen manuellen Hantierungen und den hohen Temperaturen bei praktisch atmosphärischen Verhältnissen im Ofen.

The described method has various innovations and serious advantages over what is known so far:

• 1. The mercury is expelled from the feed material in a closed, sealed thin-film evaporator under vacuum. or at <1 bar. This means that instead of electrical heating at normal pressure and 550 ° C with an organic heat transfer fluid of 360 ° C in the final stage can be heated. The good heat transfer of the water vapor condensation can be exploited in the entrance zone, in which water is to be evaporated.
• 2. If there are leaks in the thin-film evaporator, only leakage air can get inside, but no mercury vapors can escape to the outside. This significantly increases the safety of plant operations for occupational safety and emissions protection issues. In previous processes, there was a fire risk in the last baking phase when air penetrated, in which anhydrous activated carbon was exposed to temperatures above 500 ° C. This risk of fire does not exist in the method according to the invention due to lower process temperatures in vacuum operation or at <1 bar.
• 3. The water and mercury vapors drawn off in the upper part of the thin-film evaporator are subjected to washing in the form of a suspension by the injected aqueous feed. As a result, less solid material is carried over into the subsequent process steps of the condensation. Dry activated carbon dust, which is most easily carried by a gas / vapor stream, does not occur in the upper part of the thin-film evaporator. This is a major advantage of this continuously charged thin-film evaporator compared to the batch process in an oven, where after the phase of evaporation of water, dry activated carbon is always in the area of the gas / steam extraction lies.
• 4. In the thin film evaporator according to this method, an intensive mass and heat exchange takes place through
  • fine atomization of the suspension slurried for this purpose. The feed is not in a resting layer on tray plates,
  • constant swirling and movement of the material to be processed. There are no layers of crust on the surface that severely hinder the mass and heat transfer of the lower layers, as is the case with a batch process of oven trays,
  • evaporating water as a transport medium for Hg. In the furnace process, further water addition was prohibited because of the high electrical heating costs for the evaporation of the same,
  • Stripping gas metered into the lower part of the thin-film evaporator via the cooler as a transport medium or to reinforce the partial pressure drop for mercury in the lower, water-free area. Such addition of stripping gas was not possible in the batch-operated furnace process because too much activated carbon dust would be entrained or there would be a fire risk at the high temperatures when air was added.
  In this way, significantly lower residual Hg contents can be achieved than in the batch furnace process and the expectation is justified that the treated material can be burned like coal dust and does not have to be disposed of as waste.
• 5. It is a continuous process in which
  • not having to heat and cool large quantities of steel as ballast as with every batch and for which there was practically no possibility of heat recovery,
  • the transport of the feed from approach to Filling in closed equipment can be done by mechanical equipment - and not by manual work of the operating personnel. A much higher level of precaution with regard to occupational safety and occupational safety for the operating personnel is thus realized as an inherent property of this method.
    This makes it much easier for the operating personnel to comply with the biological working substance tolerance values for mercury than was the case under the conditions of the previous method with its manual handling and the high temperatures at practically atmospheric conditions in the furnace.

A device for carrying out the method according to the invention is shown in FIG.
It is a thin-film evaporator 1 with a rotary atomizer 2. The jacket 3 of the thin-film evaporator contains a rotating device 4. The thin-film evaporator 1 has a first operating fluid chamber 5 for condensing water vapor, a second operating fluid chamber 6 and a third operating fluid chamber 7, each for hot oil as organic Heat transfer fluid. The device has a heat exchanger 8 for water heating. In addition, there is an injection condenser 9, a separator / decanter 10, a washing column 11, and a separator / decanter 12. The system has a vacuum pump 13 and a batch and preheating container 14. A mill 15 is used to prepare the material for wet grinding, which is connected to a circulation pump 16. There is also a diaphragm pump 17. The thin-film evaporator 1 is connected to a cooling device 18, which in turn is connected to discharge containers 19 and 20 from the vacuum.

There is also a pneumatic conveying device 21 and a submersion vessel 22 with a barometric height difference from the separator / decanter 10. The system also has coolers 24 and 26.

A

quecksilberhaltiges Aufgabegut

B

behandeltes Gut, entquickt

C

Abgas

G

Gas

HG

Quecksilber

HO

Heißöl (organische Wärmeträgerflüssigkeit)

KO

Kondensat

KW

Kühlwasser

KM

Kaltmedium (Kältemittel, Kaltwasser)

PF

Prozeßflüssigkeit

WA

Wasser

WD

Kondensierenden Wasserdampf

WF

Waschflüssigkeit

WW

Warmwasser

The name of the process media and equipment can be seen in the following table:

A

feed containing mercury

B

treated good, disenchanted

C.

Exhaust gas

G

gas

HG

mercury

HO

Hot oil (organic heat transfer fluid)

KO

condensate

KW

cooling water

KM

Cold medium (refrigerant, cold water)

PF

Process fluid

WA

water

WD

Condensing water vapor

WF

Washing liquid

WW

Hot water

List of reference numbers

1

Thin film evaporator

2nd

Rotary atomizer

3rd

Jacket of the thin film evaporator

4th

Rotating device in the thin film evaporator

5

first equipment room for condensing water vapor

6

second operating room hot oil (organic heat transfer fluid)

7

third operating room hot oil (heat transfer fluid)

8th

Heat exchanger water heating

9

Injection condenser

10th

Separator / decanter

11

Wash column

12th

Separator / decanter

13

Vacuum pump

14

Batch and preheating container (2 times including items 15 to 17 for continuous loading of item 1)

15

Mill for wet grinding

16

Circulation pump

17th

Diaphragm pump

18th

Cooler

19th

Removal container from the vacuum

20th

Removal container from the vacuum

21

Pneumatic conveyor

22

Immersion vessel in barometric height difference to item 10

23

Circulation pump

24th

cooler

25th

Circulation pump

26

cooler

Claims (3)

1. A process for the purification by distillation of substances and/or mixtures of substances containing mercury, in which the feed material containing mercury is moved, the feed material is firstly wet ground, water being optionally added, and a suspension is formed with a dry substance content of <= (less than/equal to) 42 % by weight, the suspension is then sprayed in the upper region of a vertically stationary film evaporator on to the indirectly heated inner wall thereof, the internal pressure of which is lower than 1 bar or is under vacuum,
   and before the suspension is introduced into the film evaporator it is heated to a temperature which is not lower than 10 K below the vaporisation point of the liquid constituents of the suspension which boil the soonest - calculated at the pressure prevailing in the film evaporator -, at or above this temperature but not higher than would correspond to a spontaneous vaporisation of 10 % of the liquid upon expansion to the pressure prevailing in the film evaporator,
   the suspension sprayed on to the inner wall of the film evaporator, which is continuously scraped by a rotating device disposed inside the film evaporator and after the scraping in each case is brought into contact with different locations of the inner wall,
   at the start of its conveying travel is exposed to a low temperature level and to a higher temperature level downstream, the low temperature level being attained by indirectly heated walls of the film evaporator by means of condensing water vapour and the higher temperature level by indirect heating with a heat-transfer fluid in a temperature range of 250 to 370°C,
   the liquid of the suspension sprayed in the upper part of the film evaporator exerts a washing action on the vapours and gases flowing countercurrently which are drawn off in the upper part of the film evaporator as Hg vapour and water vapours,
   the evaporating substances, substantially mercury and water, after leaving the upper end of the film evaporator pass through:

   - a heat exchanger for heat recovery,

   - a condensing means ,

   - washing with water in a packed column,

   - a vacuum station,

   - a waste-gas purification with acid washing, caustic soda wash, water wash, heating by indirect heat exchange with hot water, and

   - an activated-carbon adsorber,

   specific stripping gas is admitted in the lower part of the film evaporator via a cooler, and a dry substance substantially free of Hg and liquid is delivered at the lower end of the film evaporator.
2. A process according to Claim 1, characterised in that a suspension with a dry substance content of 10 to 30 % by weight is prepared by wet grinding of the feed material.
3. A process according to Claim 1 or Claim 2, characterised in that the higher temperature attained by indirect heating is 300 to 350°C.

Images